Process for the manufacturing of slabs or blocks of conglomerate of stone granulate and polyester resin

ABSTRACT

In the manufacture of articles in slabs or blocks according to so-called Bretonstone technology, a polyester resin is employed, free of reactive solvents, formed by the reaction between an epoxidised triglyceride and at least one carboxylic anhydride.

The present invention regards the manufacture of articles of aconglomerate and more in particular a process for the manufacture ofslabs and blocks starting from a mixture comprising granulated stonematerial or the like and a resin-based binder.

A process for the manufacture of articles in form of blocks and slabs ofthe aforesaid type has been known for years, also known with the genericname of

Bretonstone technology, in which an initial mixture is prepared composedof granulated stone material or inorganic or organic stone-likematerial, having a selected granulometry, and of a hardenableresin-based binder.

This mixture is deposited on a temporary support or in a mould, havingthe dimensions of the final article, and is subjected to a vacuumcompression step, with the accompanying application of a vibratorymotion at pre-established frequency.

The resulting raw article is then transferred to a hardening step, atthe end of which it has the desired mechanical characteristics.

The resulting slab, which can be obtained from a block by means ofsawing, is then sent to the finishing working (sizing, smoothing,polishing and the like).

For more information and technical details regarding the Bretonstonetechnology, one should examine the European patent No. 786 325 filed inthe name of Marcello Toncelli and the International patent applicationNo. PCT/EP2006/062120 filed by the same applicant, both incorporatedhere for reference purposes.

In the production of agglomerate products based on stone or stone-likegranules, according to the Bretonstone technology, one can use resins ofstructural type. These include polyester resins, acrylic resins, epoxyresins etc.

Using these resins in the Bretonstone technology, one can obtain goodquality products with distinguishing characteristic specifications.

The most widespread products are the agglomerates comprisingorthophthalic-based polyester resins, diluted with a monomer of reactivesynthesis such as styrene.

It is remarkable that the polyester resin is a synthesis product derivedfrom oil, whose problems are well-known.

Moreover, the presence of the styrene monomer as reactive solvent in thepolyester resin and thus in the mixture leads to several differentenvironmental problems, connected to its harmful nature and to the riskof explosion tied to the high volatility; sophisticated and costlydevices are in fact necessary for collecting and removing the styrenevapours in order to comply with the increasingly strict emission laws.

A further problem, up to now unresolved, is that of the ratherconsiderable yellowing to which the articles (obtained from polyesterresin with solvent) are subjected when exposed to ultraviolet rays. Itis evident that this long-term problem, especially for the articles tobe applied as external coverings of buildings, affects the article'saesthetic characteristics.

The object of the invention is therefore of making articles according tothe Bretonstone technology, in which the mechanical and aestheticcharacteristics obtainable using the previously mentioned binder resinsare maintained while at the same time the above-described problems areovercome; in particular the presence of styrene in the mixture iseliminated.

Such object is attained with a process of the previously identified typewhich is characterised in that in the final article, the binder resin isa polyester resin lacking reactive solvent and formed by reactionbetween at least one epoxidised triglyceride and at least one carboxylicanhydride.

This is therefore a type of polyester resin used for the first time inthe field of Bretonstone technology, wherein at least 50% by weight isobtained from raw materials of renewable origin, in particular vegetalorigin, such as the epoxidised triglycerides, and from at least onecarboxylic anhydride.

For detailed information on the polyester resins used in the presentinvention, reference can be made to the published German patentapplication No. DE10148672 A1.

Regarding the first previously mentioned component, several furtherspecifications are appropriate.

Natural products, especially those of vegetal origin, contain a greatquantity of fatty acids esterified with glycerine to form thetriglycerides which can be extracted by means of known techniques.

In nature, fatty acids are almost never freely present, but are insteadbound to an alcohol, the glycerol. Glycerol can bind from 1 to 3 fattyacids: there are therefore mono-, di-, and triglycerides of the fattyacids.

The fatty acids are composed of a chain of carbon atoms bound tohydrogen atoms, a chain which usually has a terminal bond with oxygen(O) or hydrogen and oxygen (OH).

The fatty acids are divided into short chain fatty acids (48 carbonatoms), medium chain fatty acids (8÷14 carbon atoms) and long chaincarbon atoms (14÷24 carbon atoms), as well as into saturated fats,monounsaturated fats and polyunsaturated fats.

The latter subdivision is very important, since the fatty acids havedifferent physical and chemical properties depending on the level ofunsaturation.

If the triglycerides are predominantly composed of saturated fatty acids(palmitic and stearic acid) or monounsaturated acids (oleic acid), thenthese compounds are solid at room temperature and are called ‘fats’, andin particular are of animal origin (lard, tallow).

If the triglycerides are predominantly composed of unsaturated fattyacids, mono-unsaturated (palmitoleic, oleic, gadoleic acid) orpolyunsaturated acids (linoleic, linolenic acids), then these compoundsare liquids at room temperature and are called ‘oils’, and in particularare of vegetal origin (olive seed oil, linseed oil, soybean oil, cornoil).

The saturated fatty acids have a linear spatial configuration whichpermits their arrangement in an ordered manner: this arrangementfacilitates molecular interactions (hydrogen bridges) and consequentlythey have a high melting point.

The mono- and polyunsaturated fatty acids, due to the double bond whichcreates an electrostatic unbalance, do not have linear but rathersinuous molecules, so that, since they are unable to arrange themselvesin an ordered manner, there are lesser bonds between the molecules andthus the melting temperature is lower. The greater the number of doublebonds, the lower the melting temperature.

For use in the present invention, these oils are subjected to anepoxidation reaction of the double bonds present (a reaction which isper se well known), as in the following schematic representation:

As regards the anhydride component, the chemical nature of theseanhydrides (aliphatic or aromatic) affects the operational parametersand consequently also the final characteristics of the obtained resin.As an example, the formulas of two anhydrides are reported below, namelyan aliphatic anhydride or of a saturated dicarboxylic acid, and anaromaticanhydride, obtained from an unsaturated dicarboxylic acid:

For the objects of the present invention, the following anhydrides canbe used (indicated as a not limiting example): pyromellitic anhydride,maleic anhydride, succinic anhydride, hexahydrophthalic anhydride,phthalic anhydride, anhydride of norbornene dicarboxylic acid, adipicanhydride, glutaric anhydride, methylphthalic anhydride,1,2-cyclohexyldicarboxylic anhydride,3-methyl-1,2-cyclohexyldicarboxylic anhydride,4-methyl-1,2-cyclohexyldicarboxylic anhydride, mixture of3-methyl-1,2-cyclohexyldicarboxylic and4-methyl-1,2-cyclohexyldicarboxylic anhydrides,methyl-tetrahydrophthalic anhydride, tetrahydrophthalic anhydride,methyl-5-norbornene-2,3-dicarboxylic anhydride, dodecenyl-succinicanhydride and mixtures of the same.

The mixture of epoxidised fatty acids and of one or more anhydrides, inthe presence of an initiator and at a temperature between 80-180° C.depending on the additives used, solidifies and hardens.

The reaction diagram is reported below:

As indicated in the reaction diagram, in the process to form the resinsthe presence of a catalyst initiator is necessary, which, according tothe nature and quantity, acts by reducing both the reaction times andthe process temperatures.

The following can be listed from among the possible initiators: halidesof alkaline metals, organometallic compounds of aluminium, zinc and tin,halides of quaternary ammonium, aliphatic and aromatic amines, boron andtitanium based complexes.

The hardening of the resin with siliceous or calcareous particles leadsto an agglomerate product with characteristics comparable to thoseobtained with polyester resins dissolved in a reactive syntheticmonomer, both from the chemical and physical standpoint.

In the preferred embodiment of the present invention, since epoxidisedoil is nearly completely saturated, use is preferred of aliphaticanhydrides since the resulting polyester resin is particularly resistantto the yellowing caused by the ultraviolet rays.

Among the advantages of the present invention, the use of a rawmaterial—the triglycerides of natural fatty acids—available in abundancefrom natural sources must be emphasized, so that the process of thepresent invention is also advantageous from the economic standpoint.

The following non-limiting example illustrates the process of thepresent invention:

A slab was manufactured according to Bretonstone technology having thefollowing composition by volume:

-   -   Resin: 19%    -   325-mesh quartz filler: 23%    -   0.1-1.2 mm quartz granules: 58%

The composition by weight of the resin was:

-   -   Epoxidised linseed oil: 55%    -   Methylcyclohexane dicarboxylic anhydride: 20%    -   Norbonene-dicarboxylic anhydride: 21%    -   1-Methylimidazole in alcohol solution: 4%

The slab was treated in an oven at 140° C. for 40 minutes. Aftercooling, the following physical characteristics were verified:

-   -   Bending strength: 59 N/mm²    -   Deep abrasion resistance: 225 mm³    -   UV treatment for 500 hours: does not yellow

It is noted that the mechanical characteristics are corresponding tothose of a similar article made of a conventional synthesis polyesterresin with styrene.

The article, morever, does not yellow if exposed to UV rays for 500hours, unlike an analogous article made of a conventional synthesispolyester resin with styrene.

It should be noted that the Bretonstone technique also permits to makearticles in block form, subsequently destined for sawing and finishingoperations like the normal natural stone blocks extracted fromquarriesI. The present invention, as defined in the subsequent claims,is equally applicable to the manufacture of such blocks.

What is claimed is:
 1. A method of manufacturing an article in a form ofone of slabs and blocks, the article comprising an initial mixture ofany stone or stone-like granulate material and a hardenable binderresin, stone or stone-like granulate material comprising a selectedgranulometry; the binder resin comprising a polyester resin, thepolyester resin lacking a reactive solvent, the polyester resin beingformed by reaction between at least one epoxidised triglyceride and atleast one carboxylic anhydride; the mixture having a vacuum-compressedand vibratory-motion dense structure; the method comprising the stepsof: (a) preparing the initial mixture; (b) depositing the initialmixture on one of a temporary support or a mould as a deposited mixture,the one of a temporary support and mould comprising dimensions of thearticle; (c) vacuum compressing the deposited mixture while accompanyingapplication of vibratory motion at a pre-established frequency to formthe vacuum-compressed and vibratory-motion dense structure; and (d)hardening the binder resin at a temperature ranging from 80 to 180degrees Centigrade to form the article; wherein step (a) is performed bymixing the stone or the stone-like granulate material and the polyesterresin forming components comprising the at least one epoxidisedtriglyceride and the at least one carboxylic anhydride.
 2. The method ofclaim 1, wherein the at least one carboxylic anhydride is selected fromone of a methyl-tetrahydrophthalic anhydride, a tetrahydrophthalicanhydride, or a mixture of a methyltetrahydrophthalic anhydride and atetrahydrophthalic anhydride.
 3. The method of claim 1, wherein the atleast one carboxylic anhydride is selected fromtetrahydro-4-methylphthalic anhydride;1,2,3,6-tetrahydro-3-methylphthalic anhydride;1,2,3,6-tetrahydrophthalic anhydride; and mixtures thereof.
 4. Themethod of claim 1, wherein the at least one epoxidised triglyceride isselected from among triglycerides of unsaturated fatty acids, mono- orpoly-unsaturated that are liquid at room temperature.
 5. The method ofclaim 2, wherein the at least one epoxidised triglyceride is selectedfrom among triglycerides of unsaturated fatty acids, mono- orpoly-unsaturated that are liquid at room temperature.
 6. The method ofclaim 3, wherein the at least one epoxidised triglyceride is selectedfrom among triglycerides of unsaturated fatty acids, mono- orpoly-unsaturated that are liquid at room temperature.
 7. The method ofclaim 1, wherein the initial mixture comprises a catalyst initiator. 8.The method of claim 2, wherein the initial mixture comprises a catalystinitiator.
 9. The method of claim 3, wherein the initial mixturecomprises a catalyst initiator.
 10. The method of claim 7, wherein thecatalyst initiator is selected from among halides of alkaline metals,organometallic compounds of aluminum, zinc and tin, halides ofquaternary ammonium, aliphatic and aromatic amines, boron and titaniumbased complexes.
 11. The method of claim 8, wherein the catalystinitiator is selected from among halides of alkaline metals,organometallic compounds of aluminum, zinc and tin, halides ofquaternary ammonium, aliphatic and aromatic amines, boron and titaniumbased complexes.
 12. The method of claim 9, wherein the catalystinitiator is selected from among halides of alkaline metals,organometallic compounds of aluminum, zinc and tin, halides ofquaternary ammonium, aliphatic and aromatic amines, boron and titaniumbased complexes.
 13. The method of claim 9, wherein the catalystinitiator is selected from among halides of alkaline metals,organometallic compounds of aluminum, zinc and tin, halides ofquaternary ammonium, aliphatic and aromatic amines, boron and titaniumbased complexes.
 14. The method of claim 1, wherein the reaction offormation of polyester resin and hardening takes place at a temperatureof 140° C.
 15. An article in the form of a slab or block, the articlecomprising: a mixture of any stone or stone-like granulate material anda hardenable binder resin, stone or stone-like granulate materialcomprising a selected granulometry; the binder resin comprising apolyester resin, the polyester resin lacking a reactive solvent, thepolyester resin being formed by reaction between at least one epoxidisedtriglyceride and at least one carboxylic anhydride; the mixture having avacuum-compressed and vibratory-motion dense structure.
 16. The articleof claim 15, wherein the at least one carboxylic anhydride is selectedfrom one of a methyl-tetrahydropthtalic anhydride, a tetrahydropthtalicanhydride, or a mixture of a methyltetrahydropthtalic anhydride and atetrahydropthtalic anhydride.
 17. The article of claim 15, wherein theat least one carboxylic anhydride is selected fromtetrahydro-4-methylphthalic anhydride;1,2,3,6-tetrahydro-3-methylphthalic anhydride;1,2,3,6-tetrahydrophthalic anhydride; and mixtures thereof.
 18. Thearticle of claim 15, wherein the epoxidised triglyceride is selectedfrom among triglycerides of unsaturated fatty acids, mono- orpoly-unsaturated which are liquid at room temperature.
 19. The articleof claim 15, wherein the anhydride is selected from among pyromelliticanhydride, maleic anhydride, succinic anhydride, hexahydrophthalicanhydride, phthalic anhydride, anhydride of norbornene dicarboxylicacid, adipic anhydride, glutaric anhydride, methylphthalic anhydride, 1,2-cyclohexyldicarboxylic anhydride, 3-methyl-1, 2-cyclohexyldicarboxylicanhydride, 4-methyl-1, 2-cyclohexyldicarboxylic anhydride, mixture of3-methyl-1, 2-cyclohexyldicarboxylic and 4-methyl-1,2-cyclohexyldicarboxylic anhydrides, methyl-tetrahydrophthalicanhydride, tetrahydrophthalic anhydride, methyl-5-norbornen-2,3-dicarboxylic anhydride, dodecenyl-succinic anhydride and mixtures ofthe same.
 20. The article of claim 15, wherein the mixture comprises acatalyst initiator.
 21. The article of claim 20, wherein the catalystinitiator is selected from among halides of alkaline metals,organometallic compounds of aluminum, zinc and tin, halides ofquaternary ammonium, aliphatic and aromatic amines, boron and titaniumbased complexes.